It is sometimes desired to prepare composites of polyurethane bonded to cured rubber for various purposes, particularly where it is desired to obtain the advantages of the properties each or both of such materials in an individual application.
For example, it may be desired to provide a vehicular tire with a rubber carcass having an outer circumferential tread of polyurethane.
It may also be desired to provide a vehicular tire with a cured rubber tread and a polyurethane carcass.
Additionally, other products, including various industrial products may be desired as laminates of cured rubber and polyurethane.
However, particularly for such composites which are normally expected to experience a considerable amount of flexing, compression and various degrees of distortion during their use, an important point of early failure can be the interface between the cured rubber substrate and the polyurethane.
Although the relationship between the two types of materials is complex and depends upon many factors, it is important to appreciate that effectively adhering a relatively polar (high surface energy) polyurethane substance to the surface of a relatively non-polar (low surface energy) cured rubber substrate can be difficult.
Various adhesive systems have been tried and sometimes suggested for such purpose. However, for many applications, the resulting bond strengths are simply insufficient to provide an effective composite laminate which will not easily delaminate under extensive working conditions.
Therefore, it is an aspect of this invention to provide a composite of a polyurethane bonded to the surface of a cured rubber substrate.